1. Field of the Invention
The present invention relates to an optical information recording and playback apparatus which performs recording and playback using a light beam on an optical information recording medium having a transparent protective layer.
2. Description of the Related Art
Heretofore, it is known to provide an optical information recording and playback apparatus which performs recording and playback using a light beam on an optical information recording medium having a transparent protective layer, wherein the recording and playback is performed by scanning a light spot with its center displaced from the centerline of the information track on the optical information recording medium. An example of this type of optical information recording and playback apparatus is disclosed in Japanese Unexamined Patent Publication with a laid-open No. 8-77583. The configuration and features of this apparatus will be described below.
FIG. 7 is a diagram showing the configuration of a rewritable magneto-optical disk apparatus. In FIG. 7, reference numeral 41 is a magneto-optical disk, the information recording medium, formed from a transparent substrate of glass or plastic material with a magnetic film 42 formed thereon. The magneto-optical disk 41 is mounted on the rotational shaft of a spindle motor 43 and rotated at a prescribed speed by the rotation of the spindle motor 43. Below the optical information recording medium 41 is disposed an optical head 44, while a bias magnet 53 is disposed above the medium at a position opposite the optical head 44.
The optical head 44 contains a semiconductor laser 45 as a light source for recording and playback; when recording information, the light beam of the semiconductor laser 45 is modulated by a laser driving circuit not shown in accordance with the information signal to be written. The light beam emitted from the semiconductor laser 45 is first made parallel by a collimator lens 46, and then passes through a polarization beam splitter 47 and enters an objective lens 48. The incident light beam is converged by the objective lens 48 and focused as a microscopic spot onto the magnetic film 42 of the magneto-optical disk 41. In the meantime, a magnetic field oriented in a particular direction is applied from the bias magnet 43 to the magneto-optical disk 41, and a series of information bits is recorded by the application of this magnetic field and the projection of the modulated light beam.
The light beam projected on the magneto-optical disk 41 is reflected at the medium surface thereof. The reflected light again passes through the objective lens 48 and enters the polarization beam splitter 47 at whose polarization plane the light is reflected toward a beam splitter 49, thus being separated from the light coming from the semiconductor laser 45. The light beam reflected into the beam splitter 49 is separated into two beams, one of which is passed through a sensor lens 50 and received by a photosensor 51. The received light signal of the photosensor 51 is fed to an AT/AF circuit (autotracking, autofocus control circuit) 52 via an AT offset circuit 59 described later. Based on this signal, the AT/AF circuit generates a tracking error signal and a focus error signal. Using the thus generated tracking error signal and focus error signal, tracking control and focus control are performed by driving an objective lens actuator 54 and thereby moving the objective lens 48 in the tracking and focusing directions.
On the other hand, when playing back information recorded on the magneto-optical disk 41, the light beam of the semiconductor laser 45 is set at a reading power not high enough to affect the recorded information, and this reading light beam is directed to the intended track to read the recorded information. More specifically, the reading light beam reflected from the surface of the optical information recording medium is passed through the objective lens 48, the polarization beam splitter 47, the beam splitter 49, and a sensor lens 55, and received by a photosensor 56.
Next, off-tracking control will be described. Reference numeral 57 is an amplitude detection circuit for detecting the amplitude of a playback signal based on the received signal of the photosensor 56. The amplitude detection circuit 57 detects cross talk and the amplitude of the playback signal when determining the off-track direction of the reading light beam, and also when determining the amount of off-tracking. The detected values are fed into a CPU 58 via an A/D converter contained therein. The CPU 58 is a processor circuit for controlling various parts of the apparatus. When the magneto-optical disk 41 is loaded into the apparatus, the CPU 58 controls the various parts to control the off-track direction and off-track amount of the reading light beam. Based on instructions from the CPU 58, the AT offset adding circuit 59 applies an offset to the AT/AF circuit 52 to displace the reading light beam off-track in the desired direction by the desired amount.
Means for determining the off-track direction will be described. When the magneto-optical disk 41 is tilted toward its outer circumference relative to the objective lens 48, as shown in FIG. 8(a), a crescent-shaped secondary spot 801b is formed on the disk surface at a position outside the main spot 801a and displaced toward the outer circumference, resulting in increased cross talk from the outer track. On the other hand, when the magneto-optical disk 41 is tilted toward its inner circumference relative to the objective lens 48, as shown in FIG. 8(b), a crescent-shaped secondary spot 802b is formed on the disk surface at a position outside the main spot 802a and displaced toward the inner circumference, resulting in increased cross talk from the inner track.
Accordingly, by measuring the amount of cross talk from each of the adjacent tracks, the tilting direction of the magneto-optical disk 41 relative to the objective lens 48 can be identified, and thus the off-track direction of the light spot to reduce the amount of cross talk can be determined. More specifically, in the case of FIG. 8(a), the outer circumferential direction is determined as the off-track direction, and in the case of FIG. 8(b), the inner circumferential direction is determined as the off-track direction.
A prior art example of determining the off-track direction will be described below. A longest pattern signal is recorded in a test area provided on a magneto-optical disk. Then, its adjacent tracks are played back, and the amplitudes of the playback signals are compared. Based on the result of the comparison, the relative tilting direction of the optical information recording medium can be identified, and thus-the off-track direction of the light spot to reduce the amount of cross talk can be determined.
Next, means for determining the off-track amount will be described. While varying the off-track amount, a reading light beam is projected a predetermined number of times onto the track of the test area where the longest pattern signal is recorded. The off-track amount is obtained from the playback signal detected at this time or from the amount of cross talk leaking from specific tracks obtained by playing back the adjacent tracks.
However, the off-track amount that maximizes the amplitude of the playback signal does not necessarily coincide with the off-track amount that minimizes the cross talk; therefore, it is desirable that the off-track amount that maximizes the difference between the two quantities, as shown in FIG. 9, be determined as the optimum value.
Operation will be described when playing back information recorded on the magneto-optical disk 41 by using the thus determined off-track direction and off-track amount.
First, the CPU 58 reads the off-track direction and off-track amount from its internal memory and, based on the direction and amount, controls the AT offset adding circuit 59. For example, when the off-track direction is the inner circumferential direction, and the off-track amount is a prescribed number of micrometers, the corresponding control signal is applied from the CPU 58 to the AT offset adding circuit 59. Upon receiving the control signal, the AT offset adding circuit 59 applies an offset corresponding to the off-track direction and off-track amount to the AT/AF circuit 52. The AT/AF circuit 52 then supplies a driving signal corresponding to the offset to the objective lens actuator 54, and the objective lens 48 is controlled in accordance with the driving signal. The reading beam emitted from the semiconductor laser 45 is thus displaced off-track by the prescribed number of micrometers in the inner circumferential direction of the optical information recording medium, and subsequent playback of the recorded information is performed with the reading light beam thus displaced off-track.
The above technique can be applied not only to optical information recording and playback apparatuses but also to apparatuses for playing back, for example, read-only recording media or playback apparatuses for write-once recording media.
The above-described optical information recording and playback apparatus requires the provision of a test area where a prescribed signal is recorded for the measurement of cross talk, and must be designed to be able to also handle optical information recording media that do not have such a test area.
Furthermore, the direction in which the center of the light spot on the optical information recording medium is displaced from the centerline of the information track, and which is determined so as to minimize the cross talk, is not always the direction that enhances the playback signal quality of the optical information recording and playback apparatus. There is, therefore, a need for a method that can more suitably determine the direction and amount to displace the center of the light spot.
In view of the problem associated with the prior art optical information recording and playback apparatus, it is an object of the present invention to provide an optical information recording and playback apparatus that can reduce the degradation of recording/playback signal quality caused by the tiling of the optical information recording medium relative to the light beam.
It is another object of the present invention to provide an optical information recording and playback apparatus that can shorten the time required to determine the optimum position to which the light spot is to be displaced when reducing the degradation of recording/playback signal quality caused by the tiling of the optical information recording medium relative to the light beam.
One aspect of the present invention is an optical information recording and playback apparatus comprising:
a light source;
a focusing optical system for focusing a light beam from said light source into a microscopic spot on a recording surface of an optical information recording medium having a transparent protective layer;
a light detector for receiving the light beam reflected or diffracted at the recording surface of said optical information recording medium, and for converting said received light beam into an electrical signal;
a signal circuit for converting said electrical signal into a playback information signal;
a signal circuit for generating from said electrical signal an error signal indicating a positional displacement between an information track and the light spot on the recording surface of said optical information recording medium; and
driving means for causing said light spot to follow said information track on said optical information by using said error signal,
said optical information recording and playback apparatus characterized by the inclusion of:
means for measuring the tilt of said optical information recording medium relative to said focusing optical system; and
an off-tracking circuit for displacing said light spot in a direction that reduces jitter of a playback signal obtained by playing back information recorded on said optical information recording medium from said information track, by giving an electrical offset to an error signal indicating a displacement in a direction parallel to said optical information recording medium and perpendicular to a scanning direction of said light spot, said error signal being among the error signals supplied to said driving means for causing said light spot to follow said information track on said optical information.
With this configuration, degradation of recording/playback signal quality due to the tilting of the optical information recording medium relative to the focusing optical system can be reduced.
Another aspect of the present invention is an optical information recording and playback apparatus comprising a jitter detection device for detecting the jitter of the playback signal obtained by playing back information recorded on said optical information recording medium, and wherein
the tilt of said optical information recording medium relative to said focusing optical system is measured by using the amount of increase in said playback signal jitter.
This configuration achieves the effect of being able to easily measure the amount of tilting of the optical information recording medium relative to the focusing optical system, as well as the effect of reducing the degradation of recording/playback signal quality caused by the tilting of the optical information recording medium relative to the focusing optical system.
Still another aspect of the present invention is an optical information recording and playback apparatus, wherein said means for measuring the tilt of said optical information recording medium relative to said focusing optical system is a tilt detection device comprising (1) a tilt detection light source, (2) a tilt detection focusing optical system for focusing a light beam from said tilt detection light source, and (3) a tilt detection light detector for projecting said tilt detection light beam onto said optical information recording medium, and for receiving light reflected from said optical information recording medium for conversion into an electrical signal.
This configuration achieves the effect of measuring the tilt of the optical information recording medium relative to the focusing optical system, as well as the effect of reducing the degradation of recording/playback signal quality caused by the tilting of the recording surfaced of the optical information recording medium.
Yet another aspect of the present invention is an optical information recording and playback apparatus, wherein said means for measuring the tilt of said optical information recording medium relative to said focusing optical system comprises a focus drive amount detection device for detecting a focus drive amount representing a drive amount in a direction perpendicular to said optical information recording medium, said focus drive amount being among said error signals supplied to said driving means, and wherein said tilt is measured based on said focus drive amount and a position currently being measured on said optical information recording medium.
This configuration achieves the effect of being able to easily measure the-tilt of the optical information recording medium relative to the focusing optical system, as well as the effect of reducing the degradation of recording/playback signal quality caused by the tilting of the optical information recording medium relative to the focusing optical system.
Still yet another aspect of the present invention is an optical information recording and playback apparatus, wherein said means for measuring the tilt of said optical information recording medium relative to said focusing optical system comprises a focus drive amount detection device for detecting a focus drive amount representing a drive amount in a direction perpendicular to said optical information recording medium, said focus drive amount being among said error signals supplied to said driving means, and wherein said tilt is measured based on said focus drive amount.
This configuration achieves the effect of being able to easily measure the tilt of the optical information recording medium relative to the focusing optical system, as well as the effect of reducing the degradation of recording/playback signal quality caused by the tilting of the optical information recording medium relative to the focusing optical system.
A further aspect of the present invention is an optical information recording and playback apparatus, comprising a jitter detection device for detecting the jitter of the playback signal obtained by playing back recorded information from said optical information recording medium, and wherein
said off-tracking circuit includes means for varying (1) an off-track direction, the direction in which said light spot is to be displaced, and (2) an off-track amount, the amount by which said light spot is to be displaced, in such a manner as to minimize said playback signal jitter.
This configuration achieves the effect of determining the optimum off-track position and the effect of measuring the tilt of the optical information recording medium relative to the focusing optical system, as well as the effect of reducing the degradation of recording/playback signal quality caused by the tilting of the optical information recording medium relative to the focusing optical system.
A still further aspect of the present invention is an optical information recording and playback apparatus, comprising an error rate detection device for detecting an error rate, the rate at which the playback signal obtained by playing back recorded information from said optical information recording medium is in error when reproduced from an information signal written on said optical information recording medium, and wherein
said off-tracking circuit includes means for varying (1) an off-track direction, the direction in which said light spot is to be displaced, and (2) an off-track amount, the amount by which said light spot is to be displaced, in such a manner as to minimize said error rate.
This configuration achieves the effect of determining the optimum off-track position and the effect of measuring the tilt of the optical information recording medium relative to the focusing optical system, as well as the effect of reducing the degradation of recording/playback signal quality caused by the tilting of the optical information recording medium relative to the focusing optical system.
A yet further aspect of the present invention is an optical information recording and playback apparatus, comprising a flag detection device for detecting a flag that is set when there is a certain amount of error in a certain amount of information by comparing the playback signal obtained by playing back recorded information from said optical information recording medium with an information signal written on said optical information recording medium, and wherein
said off-tracking circuit includes means for varying (1) an off-track direction, the direction in which said light spot is to be displaced, and (2) an off-track amount, the amount by which said light spot is to be displaced, in such a manner as to minimize the number of flags in said amount of information.
This configuration achieves the effect of determining the optimum off-track position and the effect of measuring the tilt of the optical information recording medium relative to the focusing optical system, as well as the effect of reducing the degradation of recording/playback signal quality caused by the tilting of the optical information recording medium relative to the focusing optical system.
A still yet further aspect of the present invention is an optical information recording and playback apparatus, comprising an RF signal detection device for detecting the amplitude of the playback signal obtained by playing back recorded information from said optical information recording medium, and wherein
said off-tracking circuit includes means for varying (1) an off-track direction, the direction in which said light spot is to be displaced, and (2) an off-track amount, the amount by which said light spot is to be displaced, in such a manner as to maximize said playback signal amplitude.
This configuration achieves the effect of determining the optimum off-track position and the effect of measuring the tilt of the optical information recording medium relative to the focusing optical system, as well as the effect of reducing the degradation of recording/playback signal quality caused by the tilting of the optical information recording medium relative to the focusing optical system.
An additional aspect of the present invention is an optical information recording and playback apparatus, wherein said off-tracking circuit includes means for setting the off-track amount, the amount by which said light spot is to be displaced, as fixed values providing one value on the inside of said information track and one value on the outside thereof as viewed in the direction normal to the scanning direction of said light spot.
This configuration achieves the effect of reducing the time required to determine the off-track amount, the effect of determining the off-track position, and the effect of measuring the tilt of the optical information recording medium relative to the focusing optical system, as well as the effect of reducing the degradation of recording/playback signal quality caused by the tilting of the optical information recording medium relative to the focusing optical system.
A still additional aspect of the present invention is an optical information recording and playback apparatus, wherein said off-tracking circuit includes means for setting the off-track amount, the amount by which said light spot is to be displaced, as fixed values providing more than one value on the inside of said information track and more than one value on the outside thereof as viewed in the direction normal to the scanning direction of said light spot.
This configuration achieves the effect of reducing the time required to determine the off-track amount, the effect of determining the off-track position, and the effect of measuring the tilt of the optical information recording medium relative to the focusing optical system, as well as the effect of reducing the degradation of recording/playback signal quality caused by the tilting of the optical information recording medium relative to the focusing optical system.
A yet additional aspect of the present invention is an optical information recording and playback apparatus, wherein said off-tracking circuit includes:
means for determining an off-track direction, the direction in which said light spot is to be displaced, as (1) a direction moving toward an inner circumference of said optical information recording medium when said inner circumference of said optical information recording medium, compared with an outer circumference thereof, is positioned closer to an incidence side of said focusing optical system because of the tilting of said optical information recording medium relative to said focusing optical system and (2) a direction moving toward said outer circumference of said optical information recording medium when said outer circumference, compared with said inner circumference, is positioned closer to the incidence side of said focusing optical system because of the tilting of said optical information recording medium relative to said focusing optical system; and
means for varying an off-track amount, the amount by which said light spot is to be displaced, in accordance with the degree of the tilting of said optical information recording medium relative to said focusing optical system.
This configuration achieves the effect of reducing the time required to determine the off-track direction, the effect of determining the off-track position, and the effect of measuring the tilt of the optical information recording medium relative to the focusing optical system, as well as the effect of reducing the degradation of recording/playback signal quality caused by the tilting of the optical information recording medium relative to the focusing optical system.
A still yet additional aspect of the present invention is an optical information recording and playback apparatus, wherein said off-tracking circuit includes:
means for determining an off-track direction, the direction in which said light spot is to be displaced, as (1) a direction moving toward an inner circumference of said optical information recording medium when said inner circumference of said optical information recording medium, compared with an outer circumference thereof, is positioned closer to an incidence side of said focusing optical system because of the tilting of said optical information recording medium relative to said focusing optical system and (2) a direction moving toward said outer circumference of said optical information recording medium when said outer circumference, compared with said inner circumference, is positioned closer to the incidence side of said focusing optical system because of the tilting of said optical information recording medium relative to said focusing optical system; and
means for setting an off-track amount, the amount by which said light spot is to be displaced, as fixed values providing one value on the inside of said information track and one value on the outside thereof as viewed in the direction normal to the scanning direction of said light spot.
This configuration achieves the effect of reducing the time required to determine the off-track amount, the effect of reducing the time required to determine the off-track direction, the effect of determining the off-track position, and the effect of measuring the tilt of the optical information recording medium relative to the focusing optical system, as well as the effect of reducing the degradation of recording/playback signal quality caused by the tilting of the optical information recording medium relative to the focusing optical system.
One aspect of the present invention is an optical information recording and playback apparatus, wherein said off-tracking circuit includes:
means for determining an off-track direction, the direction in which said light spot is to be displaced, as (1) a direction moving toward an inner circumference of said optical information recording medium when said inner circumference of said optical information recording medium, compared with an outer circumference thereof, is positioned closer to an incidence side of said focusing optical system because of the tilting of said optical information recording medium relative to said focusing optical system and (2) a direction moving toward said outer circumference of said optical information recording medium when said outer circumference, compared with said inner circumference, is positioned closer to the incidence side of said focusing optical system because of the tilting of said optical information recording medium relative to said focusing optical system; and
means for setting an off-track amount, the amount by which said light spot is to be displaced, as fixed values providing more than one value on the inside of said information track and more than one value on the outside thereof as viewed in the direction normal to the scanning direction of said light spot.
This configuration achieves the effect of reducing the time required to determine the off-track amount, the effect of reducing the time required to determine the off-track direction, the effect of determining the off-track position, and the effect of measuring the tilt of the optical information recording medium relative to the focusing optical system, as well as the effect of reducing the degradation of recording/playback signal quality caused by the tilting of the optical information recording medium relative to the focusing optical system.
Another aspect of the present invention is an optical information recording and playback apparatus, comprising means for splitting said optical information recording medium into a prescribed number of areas according to the amount of warping contained in said optical information recording medium, and for measuring the tilt of said optical information recording medium relative to said focusing optical system each time switching is made from one area to another.
This configuration achieves the effect of reducing the time required to determine the off-track amount, the effect of reducing the time required to determine the off-track direction, the effect of determining the off-track position, and the effect of measuring the tilt of the optical information recording medium relative to the focusing optical system, as well as the effect of reducing the degradation of recording/playback signal quality caused by the tilting of the optical information recording medium relative to the focusing optical system.
As described above, provisions are made in the present invention to determine the direction of displacement and the amount of displacement, for example, when scanning a light spot on the optical information recording medium by displacing the center of the light spot from the centerline of the information track to reduce jitter of the playback signal. The apparatus thus configured can also handle optical recording media that do not have a test area. Furthermore, the direction in which the center of the light spot is displaced and the amount of displacement can be limited, achieving the effect of reducing the time required to determine the optimum position to which the light spot is displaced.